The epithelial Na+ channel (ENaC) regulates Na+ absorption across many epithelia. In the airways of cystic fibrosis (CF) patients, ENaC is abnormally hyperactive leading to disproportionate Na+ absorption and a depletion of airway surface liquid (ASL) volume. This contributes to mucus stasis and increased incidence of airway infections that frequently lead to the death of the patient. Surprisingly, there are no existing therapies to treat abnormal ENaC activity in the lung. However, biological control of ENaC is complex, and offers several opportunities for therapeutic intervention. Using a proteomic screen, we have identified the protein SPLUNC1 as a potent allosteric inhibitor of ENaC that binds extracellularly to ENaC, reducing the amount of ENaC in the plasma membrane and subsequently limiting ENaC activity. After identifying the ENaC-inhibitory domain of SPLUNC1 we have completed screening and lead selection of a peptide for clinical development. This peptide robustly inhibits ENaC and prevents ASL hyperabsorption in CF airway cultures for 24 h following a single dose. This peptide has completed animal toxicology and is being prepared for First Time in Human dosing. CF patients currently face significant treatment burdens with an average time spent on treatment activities of 108 minutes per day. If human efficacy studies prove the benefit of the therapy predicted by cell culture and animal models then the peptide will be a disease modifying therapy impacting mucus clearance, lung infection and lung capacity when administered as a chronic therapy. To deliver these benefits to patients without adding to their treatment burden we seek to develop a dry powder inhaler (DPI) product presentation. We will demonstrate proof of concept for developing a DPI by: (i) evaluating the feasibility of spray drying our peptide to produce a respirable powder; and (ii) demonstrating the biological activity is not altered by spray drying. Completion of the proposed work will lead to a Phase II application that will be aimed at scaling the spray drying process and producing material for animal toxicology studies.